Polymers such as partially hydrolyzed polyacrylamides are known to degrade to a substantial extent, even at low concentrations, when subjected to turbulences normally present in the equipment utilized to convey such polymers from one location to another. This problem is especially acute in situations where, as in the use of such polymer solutions in the recovery of oil from subterranean oil-bearing formations, the polymer solutions are transported through a series of conduits and flow control valves prior to injection into a wellbore. Degradation of the polymer adversely affects the injectivity and mobility properties of the polymer thereby greatly diminishing its ability to satisfy the performance demands of the oil-bearing formation. When large pressure drops of the order of 50 psig and greater are required in such operations, it is common practice to use long lengths of small diameter tubing or sand packs to reduce polymer degradation. In order to vary the pressure drop by this means, it is necessary to shorten, or lengthen, the small diameter tubing, or to vary the number of sand packs. This practice is cumbersome, at best, and does not provide the degree of control necessary to attain the desired result.